The present invention relates to controllable fluids used to control interlock mechanisms and more particularly to such mechanisms wherein the controllable fluid comprises a magnetorheological fluid.
A great variety of mechanical systems are controlled by cables, push rods, or other elongated force-transmitting members. Control systems of this type are widely employed, especially in vehicular and industrial applications. Such applications include machine tools, manufacturing equipment, and materials handling systems. For reasons of safety and/or process control, it is often desirable to lock out or otherwise immobilize such control systems and thereby prevent the operation of the controlled mechanical system.
An exemplary application is the brake transmission safety interlock (BTSI) system utilized in automobiles. A BTSI system operates to prevent a vehicle's transmission from being taken out of the "park" position if the braking system is not activated. In a typical BTSI system, the shift linkage has a cable-activated locking latch. This latch must be released, typically by activating a button associated with the shifter and communicating with the latch by a cable or push rod, before the transmission may be shifted out of the "park" position. BTSI systems further include some type of immobilizing device associated with the cable and communicating with the brake system. If the brake system is not activated, then the immobilizing device prevents movement of the cable and release of the latch.
A solenoid may be used to control the mechanical linkage, as in U.S. Pat. No. 4,887,702, which describes a typical latch mechanism as well as a particular solenoid controlled BTSI system. In this system, the latch release cable is associated with the plunger of a solenoid and activation of the solenoid draws the plunger and cable into the solenoid coil, thereby preventing further motion of the cable. In its inactive state, the plunger and cable are free to move back and forth. The solenoid and other components each present a potential failure point in the system. In addition, a system with several components bears a higher production cost.
Accordingly, there is a need in the art for improved interlock mechanisms and, more particularly, for interlock mechanisms that require fewer moving parts.